Method of forming a composite article comprising steel and silver



Patented June 19,1951

STATE.

' 'Fl CE Thomas R. Holbrook, Cornelia, (3a., assignor to General Motors Corporation, Detroit, Mich, a

corporation of Delaware No Drawing. Application October 26, 1946,

Serial No. 706,074 I 6 Claims. (c1. 204-34) This invention relates to a method of forming composite articles comprising electrolytically deposited silver strongly bonded to steel through an intermediate nickel coating. The invention is particularly useful in forming steel-backed silver plated bearings.

It has been found desirable heretofore in forming composite articles such as bearings consisting of electrolytically deposited silver supported by a carbon steel backing member to apply a nickel strike to the steel backing member and then electrolytically deposit the silver onto the nickel plated steel backing member. In certain instances the silver plated bearings may be rejected because of unsatisfactory bond or for other reasons. Such bearings have been salvaged heretofore by stripping off the silver electrolytically, then grinding or polishing off the nickel strike and then replating the bearings by applying a new nickel strike and a new electrodeposit of silver. Great care has had to be taken to remove the nickel strike in order to obtain a strong bond when the bearings are replated.

By means of the present invention it is unncessary to remove the old nickel strike before in which silver bearings or other silver plated ferrous metal articles are salvaged, the silver is first stripped in any suitable manner, for example by an electrolytic stripping operation. The silver electrolytic stripping operation can be carried out by makin the articles to be stripped the anode and using steel plates as the cathode upon which the silver deposits and falls to the bottom of the tank. A suitable silver stripping bath is one composed of 30 to 90 grams of sodium cyanide per liter of solution and 2 to 4 grams of sodium hydroxide per liter. A voltage of 6 to 9 is applied between the anode and cathode and the process is continued until all the silver is stripped off. Any other means for removing the silver may be employed.

The bearing or other article having the silver stripped therefrom and with the old nickel strike thereon is now treated cathodically in a solution consisting essentially of hydrochloric acid, water and nickel chloride within the range of 0.2 oz. to 1.5 oz. per gallon of solution. It is desirable to maintain the concentration at or below 1 oz. of

hydrous nickel chloride (NiCIZGHZO) per gallon of solution. The hydrochloric acid is preferably employed in a concentration of about 25% by volume based on commercial concentrated hydrochloric acid composed of about 37% E101 and the balance water. In other words, to obtain the 25% concentration the commercial acid would be diluted with three volumes of water. The concentration of hydrochloric acid is not critical and the percentage variation by volume of the commercial hydrochloric acid may vary from 1 to approximately 100. The smaller percentages require greater length of time for the cathodic treatment while the higher concentrations have correspondingly higher acid carry-over. This latter is expensive and requires more thorough washing and rinsing in order to prevent contamination of the next bath. Ordinarily the concentration of commercial hydrochloric acid by volume is more than 6%. The stripped steel part havin the nickel strike thereon is made the cathode in the aqueous solution of hydrochloric acid and nickel chloride and direct current passed through the solution from an anode to the stripped article as the cathode. Employing the optimum solution consisting essentially of 25% by volume hydrochloric acid and one oz. of hydrous nickel chloride per gallon of solution and with a six volt direct current power source impressed across the bath between an anode and the cathode a time of treatment of to seconds have proven very satisfactory. Where a greater or lesser concentration of hydrochloric acid is employed the time and other conditions may be adjusted as required to obtain the same or substantially the same effect as obtained with the 60 to 90 second treatment in the 25% solution.

The part as thus cathodically treated or etched is rinsed or washed in cold water and then is made the cathode in a nickel strike electrolyte of any desired type. A suitable electrolyte for the nickel strike is one composed as follows: Nickel (as metal) 60-75 gm./ 1., nickel chloride -125 gm./l. and boric acid 30-37 gm./l. The pH for a hand strike is adjusted to 1.45-1.60 while for an automatic strike a pH of 4.50 to 5.50 is maintained- Current is passed through the strike solution from an anode to the article as cathode. A maximum cathode current density of 30 amperes per square foot is applied for 45-60 seconds. This produces a satisfactory nickel strike of around .0001" in thickness.

The steel having thereon the nickel strike now has silver clectrodeposited thereon. Usually a silver strike is first applied as by means of an aqueous cyanide type of silver plating electrolyte, for example, one consisting essentially of 156-165 grams per liter of potassium cyanide (free) and 2 to 3 grams per liter of silver cyanide. In this solution a cathode current density of 25-35 amperes per square foot for a time of 10-20 seconds produces a suitable silver strike. Other silver strike solutions may be employed. After the silver strike is applied, a much thicker coating of silver is electrodeposited onto the silver strike. An aqueous solution consisting essentially of 160 to 175 grams per liter of potassium cyanide (free) 130 to 140 grams per liter of silver cyanide, and 10 to 15 grains per liter of potassium hydroxide may be used for applying the relatively thick electrodeposit of silver.

In the foregoing silver plating solution a cathode current density of 35-50 amperes per square foot produces a good adherent deposit of silver. The process is continued until the desired thickness of silver is applied. For bearings, as much as .050 silver may be deposited.

Another suitable silver plating bath is one containing potassium cyanide (free) 5t-60 gin/1., silver cyanide 50-60 gm./l. and a small amount of Supermix Brightener suhicient to obtain bright deposits of silver. A bath temperature of 90-105 F. is preferably employed. The Supermix Brightener is a solution composed substantially as follows: amnonium thiosulfate plus ainmonium polythionates, 32.5%, acetic acid 3.5 boric acid 3.5%, sodium sulfite 9:5, water the remainder. The solution has a specific gravity of 1.305 at 25 C. and a pH of 4.25 at 25 (3. In making up the silver plating solution 0.05 to 12.5 ml. of the brightener per liter of plating solution is used.

The cathodic etch in the aqueous solution of hydrochloric acid and nickel chloride makes possible a very strong bond between the original nickel strike left on the steel after the silver stripping operation and the new nickel strike. As a possible explanation of the strong bond produced by the described procedure, it appears that the nickel remaining on the steel after the silver has been stripped is very passive due to the severe oxidize-tion in the silver stripping bath and by giving the steel stripped of the silver a cathodic etch or treatment as described in the aqueous solution of hydrochloric containing the very small proportion of nickel chloride, the old passive nickel is reactivated, a very thin film of extremely active nickel is electrodeposited and the surface is in very good condition to receive the new nickel strike. The foregoing is advanced as a possible explanation of the improved results obtained by the described procedure but I do not wish to be bound by any theories in this respect.

The foregoing procedure has been found of especial advantage in salvaging defective silver bearings having a backing of steel. In this connection the following advantages are mentioned:

1. Saves all steel shells.

2. Eliminates all grinding and polishing operations heretofore employed to remove the nickel strike.

3. Eliminates returning stripped shells to receiving inspection for another inspection. Shells can be stripped and replated Without leaving plating room.

1. Saves the I. D. machining operation, I. D. plate, and steel shells on those parts which would otherwise be scrapped for defective O. D. plate.

4 In many cases shells do not have to be unmasked and masked again.

In addition to salvaging defective silver plated steel articles as described in detail above, the in vention also has application to plating new articles, bearings, for example, which comprise steel, nickel electrodeposited on the steel and silver electrodeposited on the nickel. In this embodiment of the invention the steel part is given the same cathodic treatment in the aqueous solution of hydrochloric acid containing the small propor tion of nickel chloride as described in the procedure for salvaging defective articles. The steel part as thus cathodically treated is given a nickel strike, and then has silver electrodeposited there- The steel parts prior to electrodeposition of nickel thereon may be degreased and thereafter cleaned by anodic treatment in an alkaline cleaner as in conventional practice. After rinsing as by means of cold running water the steel is then ready to be treated cathodicallly in the electrolyte consisting of the aqueous solution of hydrochloric acid and the small concentration of nickel chloride. The parts also may be rinsed in water between the several plating operations as in conventional practice to clean the parts and to prevent carry--over of one plating bath to another.

I claim:

1. A process of salvaging defective parts consisting 01" steel, a nickel strike thereon and an electrodeposit of silver on the nickel which includes, stripping the electrodeposit of silver from a defective part, cathodicall treating the part stripped of silver in a solution consisting essentially of nickel chloride, hydrochloric acid and water, said hydrochloric acid being employed in said solution in a concentration within the range oi 1% to approximately by volume based on commercially concentrated hydrochloric acid and the nickel chloride being present in a concentration within the range of 0.2 oz. to 1.5 oz. of hydrous nickel chloride per gallon of solution, then applying a nickel strike to the cathodically treated part, and thereafter electrodepositing silver onto the nickel strike.

2. A process as in claim 1 in which the hydrochloric acid is employed in a concentration of about 25% by volume of commercially concentrated hydrochloric acid, about one oz. of hydrous nickel chloride per gallon of solution is employed, a voltage of about six is applied in said cathodic treatment and direct current passed through said solution from an anode to the cathode for about sixty to ninety seconds.

3. A process of forming a composite product comprising electrodeposited silver bonded to steel through an intermediate electrodeposited coating of nickel which includes, cathodic treatment of a metal surface of the class consisting of steel and nickel plated steel in a solution consisting essentially of nickel chloride, hydrochloric acid and water, said hydrochloric acid being employed in said solution in a concentration within the range of 1% to approximately 100% by volume based on ccmmerically concentrated hydrochloric acid and the nickel chloride being present in a concen tration within the range of 0.2 to 1.5 oz. of hydrous nickel chloride per gallon of solution, then applying a nickel strike to the cathodically treated surface and thereafter electrodepositing a coating of silver onto the nickel strike.

4. A process as in claim 3 in which the hydrochloric acid is employed in a concentration of about 25% by volume of commercially concentrated hydrochloric acid, about one 02. of hydrous nickel chloride per gallon of solution is employed, a voltage of about six is applied in said cathodic treatment and direct current passed through the solution from an anode to the cathode for about sixty to ninety seconds.

5. A process of forming a combination of electrodeposited coatings on steel which includes, passing direct current from an anode to said steel as the cathode through a solution consisting essentially of nickel chloride, hydrochloric acid and water, said hydrochloric acid being employed in said solution in a concentration within the range of 1% to approximately 100% by volume based on commercially concentrated hydrochloric acid and the nickel chloride being, present in a concentration within the range of 0.2 to 1.5 oz. of hydrous nickel chloride per gallon of solution, then applying a nickel strike to said cathodically treated steel and thereafter applying an electro deposited coating of silver onto said nickel.

6. A process of treating a nickel plated steel product which includes, passing direct current from an anode to said nickel plated steel product as the cathode through a solution consisting essentially of nickel chloride, hydrochloric acid and water, said hydrochloric acid being employed in said solution in a concentration within the range of 1% to approximately 100% by volume THOMAS R. I-IOLBROOK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,373,837 Schulte Apr. 5,1921 2,285,548 Wesley June 9, 1942 2,391,039 Schaefer Dec. 18,1945 2,437,409 Tucker Mar. 9, 1948 OTHER REFERENCES Iron Age, Sept. 26, 1940, pp. 17-20.

Iron Age, Oct. 3, 1940, pp. 30-33.

(Above articles by E. J. Roehl.)

Journal of the Electrodepositors Technical Society, vol. 13 (1937), article 12, pp. 1-3 and 8 of the article, by A. W. Hothersall. 

1. A PROCESS OF SALVAGING DEFECTIVE PARTS CONSISTING OF STEEL, A NICKEL STRIKE THEREON AND AN ELECTRODEPOSIT OF SILVER ON THE NICKEL WHICH INCLUDES, STRIPPING THE ELECTRODEPOSIT OF SILVER FROM A DEFECTIVE PART, CATHODICALLY TREATING THE PART STRIPPED OF SILVER IN A SOLUTION CONSISTING ESSENTIALLY OF NICKEL CHLORIDE, HYDROCHLORIC ACID AND WATER, SAID HYDROCHLORIC ACID BEING EMPLOYED IN SAID SOLUTION IN A CONCENTRATION WITHIN THE RANGE OF 1% TO APPROXIMATELY 100% BY VOLUME BASED ON COMMERCIALLY CONCENTRATED HYDROCHLORIC ACID AND THE NICKEL CHLORIDE BEING PRESENT IN A CONCENTRATION WITHIN THE RANGE OF 0.2 OZ. TO 1.5 OZ OF HYDROUS NICKEL CHLORIDE PER GALLON OF SOLUTION, THEN APPLYING A NICKEL STRIKE TO THE CATHODICALLY TREATED PART, AND THEREAFTER ELECTRODEPOSITING SILVER ONTO THE NICKEL STRIKE. 